Sustainable NO removal and its sensitive monitoring at room temperature by electrogenerated Ni (I) electron mediator.

Online monitoring of gas pollutants in the gas phase at room temperature using an electrochemical macro gas flow sensor is challenging and important for the pollutant treatment process. In this work, for the first time, we tried to explore the homogeneous and heterogeneous application of Ni(II) (CN)42- in the KOH environment for the removal and monitoring of toxic nitric oxide gas. The homogeneous electrogenerated Ni(I) (CN)43- was effectively removing the toxic nitric oxide gas by electro scrubbing method and the novel Ni(II) (CN)42- and KOH modified electrode used for heterogeneous sensor application with high sensitivity, and reliability toward Nitric oxide gas. The sensor showed enhanced gas diffusion and high sensitivity. Scanning electron microscopy and X-ray diffraction confirmed the modification of the carbon felt electrode. In a high concentrated KOH environment, the active mediator stabilized the sensor for a long time compared to the neutral environment. The Ni(II) (CN)42- fabricated carbon felt was used to monitor the concentration of nitric oxide gas pollutant; the calculated sensitivity was approximately -0.33 mA ppm-1 cm-2. The current increased linearly with increasing nitric oxide concentration up to 12 ppm and was validated by online gas chromatography. The developed electrochemical gas flow sensor successfully monitored the unremoved nitric oxide gas at the exit from the MER electro-scrubbing process; the concentration was calculated using a calibration plot.

Enhanced electro-reduction of NO to NH3 on Pt cathode at electro-scrubber.

Besides cheaper electrodes used in NH3 product formation during NO degradation by mediated electrochemical reduction (MER), a specific electrode that can perform direct electrochemical reduction (DER) and MER of NO is an added advantage. In the present study, a Pt electrode was used to examine NO degradation through NH3 formation during the electro-scrubbing process. Initially, the DER of NO was tested on a Pt electrode to determine if the DER of NO is possible. The NO degradation by only absorption, DER on Pt, and MER using electrogenerated [Ni(I)(CN)4]3- showed that a combination of DER and MER increased the NO degradation efficiency. In addition, the online FTIR spectra obtained under different conditions showed that the product formed was NH3, either from the DER or MER during electro-scrubbing. The feed gas flow rate and feed concentration results of NH3 formation revealed an additional chemical reaction that was influenced by the Pt electrode in addition to the DER and MER processes. Furthermore, the degradation efficiency of NO when using the Pt electrode increased to 90% compared to that of the Cu electrode (65%), which showed that Pt follows a combination of DER and MER processes. Based on the gas-phase FTIR results of NH3 formation during NO degradation, higher NH3 production (0.32 mg/h) was obtained when using a Pt electrode than that using a Cu electrode (0.21 mg/h), highlighting the specificity of the Pt electrode in NH3 formation during the degradation of NO gas.

Quick vaporization of sprayed sodium hypochlorite (NaClO(aq)) for simultaneous removal of nitrogen oxides (NOx), sulfur dioxide (SO2), and mercury (Hg0).

Sodium hypochlorite (NaClO) has been widely used as a chemical additive for enhancing nitrogen oxide (NOx; NO + NO2), sulfur dioxide (SO2), and mercury (Hg0) removals in a wet scrubber. However, they are each uniquely dependent on NaClO(aq) pH, hence making the simultaneous control difficult. In order to overcome this weakness, we sprayed low liquid-to-gas (L/G) ratio (0.1 L/Nm3) of NaClO(aq) to vaporize quickly at 165 °C. Results have shown that the maximized NOx, SO2, and Hg0 removals can be achieved at the pH range between 4.0 and 6.0. When NOx and Hg0 coexist with SO2, in addition, their removals are significantly enhanced by reactions with solid and gaseous by-products such as NaClO(s), NaClO2(s), OClO, ClO, and Cl species, originated from the reaction between SO2 and NaClO(aq). We have also demonstrated the feasibility of this approach in the real flue gases of a combustion plant and observed 50%, 80%, and 60% of NOx, SO2, and Hg0 removals, respectively. These findings led us to conclude that the spray of NaClO(aq) at a relatively high temperature at which the sprayed solution can vaporize quickly makes the simultaneous control of NOx, SO2, and Hg0 possible. Implications: The simple spray of NaClO(aq) at temperatures above 165 °C can cause the simultaneous removal of gaseous NOx, SO2, and Hg0 by its quick vaporization. Their maximized removals are achieved at the pH range between 4.0 and 6.0. NOx and Hg0 removals are also enhanced by gaseous and solid intermediate products generated from the reaction of SO2 with NaClO(aq). The feasibility of this approach has been demonstrated in the real flue gases of a combustion plant.

Surfactant structural effects on mediated electrocatalytic dechlorination: Links between the micellar enhancement of dechlorination reactions and micellar properties.

Electrocatalytic dechlorination mediated by micelle-solubilized electrocatalysts has attracted considerable current interest for pollutant degradation. Aggregation in micellar assemblies and their interactions with the additives in solution are affected by the surfactant structure. By choosing appropriate surfactant molecules, the system properties may be altered to achieve enhanced dechlorination efficiency. Cetyltrimethylammonium bromide-based surfactants with different hydrocarbon lengths and headgroup structures were studied for their structural effects on [Co(I)(bipyridine)3]+-mediated dechlorination reactions. A widely used pollutants allyl chloride derivatives were studied as the substrates. The performance of the surfactants towards various dechlorination reactions was evaluated by cyclic voltammetry (CV) based on the catalytic efficiency. Key micellar parameters were determined by CV and rotating disc electrode using [Co(II)(bipyridine)3]2+ as the micelle-solubilized redox probe. The surfactants affected the dechlorination reaction to different extents, correlating well with their structure. The catalytic efficiency was explained by the interactions of the Co(II)/Co(I) with the surfactant hydrophobic tail and headgroup. This is the first report quantitatively linking the performance of the surfactants in dechlorination reactions with their molecular structure, showing that is possible to use variant surfactant structures to tune the micellar properties for their application towards the enhanced dechlorination of organic pollutants. Substrate structure-susceptibility to reduction relationships were also discussed.

Implementation of concurrent electrolytic generation of two homogeneous mediators under widened potential conditions to facilitate removal of air-pollutants.

Electro-scrubbing is being developed as a futuristic technology for the removal of air-pollutants. To date, only one homogeneous mediator for the removal of air pollutants has been generated in each experiment using a divided electrolytic flow cell in an acidic medium. This paper reports the concurrent generation of two homogenous mediators, one at the anodic half-cell containing an acidic solution and the other at the cathodic half-cell containing a basic solution. The concept was inspired by the change in pH that occurs during water electrolysis in a divided cell. A 10 M KOH electrolyte medium assisted in the electrochemical generation of low valent 14% Co1+ ([CoI(CN)5]4-) mediator formed from reduction of [CoII(CN)5]3- which was accompanied by a change in the solution 'oxidation reduction potential' (ORP) of -1.05 V Simultaneously, 41% of Co3+ was generated from oxidation of CoIISO4 in the anodic half-cell. No change in the solution ORP was observed at the cathodic half-cell when both half-cells contain 5 M H2SO4, and Co3+ was formed in the anodic half-cell. An electro-scrubbing approach based on the above principles was developed and tested on gaseous-pollutants, CH3CHO and CCl4, by Co3+ and Co1+, respectively, with 90 and 96% removal achieved, respectively.

Studies on Effective Generation of Mediators Simultaneously at Both Half-Cells for VOC Degradation by Mediated Electroreduction and Mediated Electrooxidation.

Of the several electrochemical methods for pollutant degradation, the mediated electrooxidation (MEO) process is widely used. However, the MEO process utilizes only one (anodic) compartment toward pollutant degradation. To effectively utilize the full electrochemical cell, an improved electrolytic cell producing both oxidant and reductant mediators at their respective half-cells, which can be employed for treating two pollutants simultaneously, was investigated. The cathodic half-cell was studied first toward maximum [CoI(CN)5]4- (Co+) generation (21%) from a [CoII(CN)6]3- precursor by optimizing several experimental factors such as the electrolyte, cathode material, and orientation of the Nafion324 membrane. The anodic half-cell was optimized similarly for higher Co3(SO4)2 (Co3+) yields (41%) from a CoIISO4 precursor. The practical utility of the newly developed full cell setup, combining the optimized cathodic half-cell and optimized anodic half-cell, was demonstrated by electroscrubbing experiments with simultaneous dichloromethane removal by Co+ via the mediated electroreduction process and phenol removal by Co3+ via the MEO process, showing not only utilization of the full electrochemical cell, but also degradation of two different pollutants by the same applied current that was used in the conventional cell to remove only one pollutant.

Influence of cathode on the electro-generation of peroxydisulfuric acid oxidant and its application for effective removal of SO2 by room temperature electro-scrubbing process.

Peroxydisulfuric acid oxidant (H2S2O8) was electro-generated using boron doped diamond (BDD) anode in an undivided electrolytic cell under the optimized conditions and used for the oxidative removal of gaseous SO2. The influence of the nature of cathode material on the formation yield of H2S2O8 was investigated with Ti, Pt, Zr and DSA electrodes in a flow type electrolytic cell under batch recirculation mode. Among the various cathodes employed Ti exhibited a good performance and the formation yield was nearly doubled (0.19 M) compared to the reported value of 0.07 M. The optimization of electrode area ratio between the anode and cathode brought out the fact that for nearly 8 times smaller Ti cathode (8.75:1) the achieved yield was ∼65% higher than the 1:1 ratio of anode and cathode. The highest concentration of 6.8% (0.48 M) H2S2O8 was seen for 35 cm(2) BDD anode with 4 cm(2) Ti at 20 °C with the measured redox potential value of +1200 mV. The oxidative removal of SO2 in an electro-scrubbing column attached to the online production of peroxydisulfuric acid under the optimized conditions of cell parameters shows that SO2 removal efficiency was nearly 100% for 25 and 50 ppm inlet concentrations and 96% for 100 ppm at the room temperature of 25 °C.

Effective identification of (NH4)2CO3 and NH4HCO3 concentrations in NaHCO3 regeneration process from desulfurized waste.

This work describes the quantitative analysis of (NH4)2CO3 and NH4HCO3 using a simple solution phase titration method. Back titration results at various (NH4)2CO3-NH4HCO3 ratios demonstrated that 6:4 ratio caused a 3% error in their differentiation, but very high errors were found at other ratios. A similar trend was observed for the double indicator method, especially when strong acid HCl was used as a titrant, where still less errors (2.5%) at a middle ratio of (NH4)2CO3-NH4HCO3 was found. Remaining ratios with low (NH4)2CO3 (2:8, 4:6) show high +ve error (found concentration is less) and high (NH4)2CO3 (7:3, 8:2, and 9:1) show high -ve error (found concentration is higher) and vice versa for NH4HCO3. In replacement titration using Na2SO4, at both higher end ratios of (NH4)2CO3-NH4HCO3 (2:8 and 9:1), both -ve and +ve errors were minimized to 75% by partial equilibrium arrest between (NH4)2CO3 and NH2COONH4, instead of more than 100% observed in back titration and only double indicator methods. In the presence of (NH4)2SO4 both -ve and +ve error% are completely reduced to 3±1 at ratios 2:8, 4:6, and 6:4 of (NH4)2CO3-NH4HCO3, which demonstrates that the equilibrium transformation between NH2COONH4 and (NH4)2CO3 is completely controlled. The titration conducted at lower temperature (5 °C) in the presence of (NH4)2SO4 at higher ratios of (NH4)2CO3-NH4HCO3 (7:3, 8:2,and 9:1) shows complete minimization of both -ve and +ve errors to 2±1%, which explains the complete arresting of equilibrium transformation. Finally, the developed method shows 2±1% error in differentiation of CO3(2-) and HCO3(-) in the regeneration process of NaHCO3 from crude desulfurized sample. The developed method is more promising to differentiate CO3(2-) and HCO3(-) in industrial applications.

A single catalyst of aqueous CoIII for deodorization of mixture odor gases: a development and reaction pathway study at electro-scrubbing process.

A constant generation of aqueous Co(III) active catalyst and its utility on various odor gases deodorization at electro-scrubbing process is the primary investigation. The Co(III) activation and regeneration for continuous use is established by electrochemical undivided cell in H2SO4 medium. The generated aqueous Co(III) is then applied to simultaneous deodorization of simulated odor gases, namely, ammonia, trimethylamine, hydrogen sulfide, methyl mercaptan, and acetaldehyde, for municipal waste treatment plant emissions. The electro-scrubbing process results indicated that deodorization is almost complete at a low gas flow rate of 30 L min(-1). FTIR and pH studies demonstrated that amine compounds are removed via complex formation with H2SO4 and Co(III). In the case of sulfur compounds, deodorization of methyl mercaptan and hydrogen sulfide are removed by the Co(III)-MEO (Co(III)-mediated electrocatalytic oxidation) process via the formation of acetic acid as intermediate and SO4(2-) as a product. Also, acetaldehyde deodorization results obtained by pH, total acidity and CO2 analyses evidence the process follow Co(III)-MEO. The constant generation of aqueous active Co(III) and an electro-scrubbing process offers promise as a means of removing odorous waste gases from gaseous emissions.

Nucleation and growth study of nano-PbO2 on Ti in different additives for electrocatalytic oxidation process.

Electrocrystallization of PbO2 on Ti electrode was studied in different bath solutions using cyclic voltammetry (CV), chronoamperometry (CA), and scanning electron microscopy. The cyclic voltammetry studies revealed that the addition of methanol postponed the oxygen evolution region and made over potential nucleation of PbO2 on Ti. Oxidation of PbO2 is preferred in second cycle (a peak) in other studied bath solutions, except the Nafion and aniline containing solution. In the presence of the pyrrole, the PbO2 formed at under deposition potential with less in numbers. Nafion and aniline inclusion turn the process in to progressive nucleation and growth without inhibition. On the other hand, other solutions studied are revealed the instantaneous nucleation and growth or inhibition at high potentials. Surface morphology explained that approximately equal to 300 nm sizes PbO2 particles with vertical nucleation and growth phenomena evidenced the Nafion and aniline are the important dopants. The results indicated that large current density or high potential polarization can be obtained in presence of methanol, Nafion, and aniline, which is one of the most important and necessary factors for forming high surface area PbO2 with strong adherence towards mediated electro-oxidation process.

Development of a biphasic electroreactor with a wet scrubbing system for the removal of gaseous benzene.

An efficient, continuous flow electroreactor system comprising a scrubbing column (for absorption) and a biphasic electroreactor (for degradation) was developed to treat gas streams containing benzene. Initial benzene absorption studies using a continuous flow bubble column containing absorbents like 40% sulfuric acid, 10% silicone oil (3, 5, 10 cSt), or 100% silicone oil showed that 100% silicone oil is the most suitable. A biphasic batch electroreactor based on 50 mL of silicone oil and 100 mL of activated Co(III) (activated electrochemically) in 40% sulfuric acid demonstrated that indirect oxidation of benzene is possible by Co(III). Combined experiments on the wet scrubbing column and biphasic electroreactor (BP-ER) were performed to determine the feasibility of benzene removal, which is reside in the silicone oil medium. In semidynamic scrubbing with BP-ER experiments using an aqueous electroreactor volume of 2 L, and an inlet gas flow and a gaseous benzene concentration were 10 Lmin(-1) and 100 ppm, respectively, benzene removal efficiency is 75% in sustainable way. The trend of CO2 evolution is well correlated with benzene recovery in the BP-ER. The addition of sodiumdodecyl sulfate (SDS) enhanced the recovery of silicone oil without affecting benzene removal. This process is promising for the treatment of high concentrations of gaseous benzene.

Temperature and Pressure Effects of Desalination Using a MFI-Type Zeolite Membrane.

Zeolites are potentially a robust desalination alternative, as they are chemically stable and possess the essential properties needed to reject ions. Zeolite membranes could desalinate "challenging" waters, such as saline secondary effluent, without any substantial pre-treatment, due to the robust mechanical properties of ceramic membranes. A novel MFI-type zeolite membrane was developed on a tubular α-Al2O3 substrate by a combined rubbing and secondary hydrothermal growth method. The prepared membrane was characterised by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and single gas (He or N2) permeation and underwent desalination tests with NaCl solutions under different pressures (0.7 MPa and 7 MPa). The results showed that higher pressure resulted in higher Na+ rejection and permeate flux. The zeolite membrane achieved a good rejection of Na+ (~82%) for a NaCl feed solution with a TDS (total dissolved solids) of 3000 mg·L-1 at an applied pressure of 7 MPa and 21 °C. To explore the opportunity for high salinity and high temperature desalination, this membrane was also tested with high concentration NaCl solutions (up to TDS 90,000 mg·L-1) and at 90 °C. This is the first known work at such high salinities of NaCl. It was found that increasing the salinity of the feed solution decreased both Na+ rejection and flux. An increase in testing temperature resulted in an increase in permeate flux, but a decrease in ion rejection.

Mineralization of gaseous acetaldehyde by electrochemically generated Co(III) in H2SO4 with wet scrubber combinatorial system.

Electrochemically generated Co(III) mediated catalytic room temperature incineration of acetaldehyde, which is one of volatile organic compounds (VOCs), combined with wet scrubbing system was developed and investigated. Depending on the electrolyte's type, absorption come removal efficiency is varied. In presence of electrogenerated Co(III) in sulfuric acid, acetaldehyde was mineralized to CO2 and not like only absorption in pure sulfuric acid. The Co(III) mediated catalytic incineration led to oxidative absorption and elimination to CO2, which was evidenced with titration, CO2, and cyclic voltammetric analyses. Experimental conditions, such as current density, concentration of mediator, and gas molar flow rate were optimized. By the optimization of the experimental conditions, the complete mineralization of acetaldehyde was realized at a room temperature using electrochemically generated Co(III) with wet scrubber combinatorial system.

Nano-Ag-Nafion modified Pt electrode for oxidation of volatile organic compounds: an electrochemical study.

In this work, we describe Nano-Ag-Nafion coated pt electrode for oxidation of volatile organic compound (VOC), here acetaldehyde. Electrochemically synthesized Nano-Ag-Nafion film on Pt was analyzed by electrochemically in various electrolyte solutions like nitric acid, sulfuric acid, potassium nitrate, and potassium hydroxide for its stability. High stability of Nano-Ag-Nafion film appeared in potassium hydroxide medium among electrolyte solutions studied. Electrocatalysis of acetaldehyde was occurred only in acid and neutral medium. A catalytic oxidative peak during cathodic voltammetric reduction scan was observed at 1.75 V, which, unusual redox behavior, follows EC' reaction path way between electrogenerated Ag(II) and acetaldehyde. For Nano-Ag potential applicability, a calibration plot was drawn from various concentration range of acetaldehyde to check the maximum concentration level of acetaldehyde degradation in air.

The combined removal of methyl mercaptan and hydrogen sulfide via an electro-reactor process using a low concentration of continuously regenerable Ag(II) active catalyst.

In this study, an electrocatalytic wet scrubbing process was developed for the simultaneous removal of synthetic odorous gases namely, methyl mercaptan (CH(3)SH) and hydrogen sulfide (H(2)S). The initial process consists of the absorption of CH(3)SH and H(2)S gases by an absorbing solution, followed by their mediated electrochemical oxidation using a low concentration of active Ag(II) in 6M HNO(3). Experiments were conducted under different reaction conditions, such as CH(3)SH and H(2)S loadings, active Ag(II) concentrations and molar flow rates. The cyclic voltammetry for the oxidation of CH(3)SH corroborated the electro-reactor results, in that the silver in the 6M HNO(3) reaction solution significantly influences the oxidation of CH(3)SH. At a low active Ag(II) concentration of 0.0012 M, the CH(3)SH removal experiments demonstrated that the CH(3)SH degradation was steady, with 100% removal at a CH(3)SH loading of 5 gm(-3) h(-1). The electro-reactor and cyclic voltammetry results indicated that the removal of H(2)S (100%) follows a mediated electrocatalytic oxidation reaction. The simultaneous removal of 100% of the CH(3)SH and H(2)S was achieved, even with a very low active Ag(II) concentration (0.0012 M), as a result of the high efficiency of the Ag(II). The parallel cyclic voltammetry results demonstrated that a process of simultaneous destruction of both CH(3)SH and H(2)S follows an H(2)S influenced mediated electrocatalytic oxidation. The use of a very low concentration of the Ag(II) mediator during the electro-reactor process is promising for the complete removal of CH(3)SH and H(2)S.

Using RuO(2) anode for chlorine dioxide production in an un-divided electrochemical cell.

Chlorine dioxide is a well known powerful disinfectant. Although there are several chemical and electrochemical methods developed for on-line chlorine dioxide generation, the details are mostly confined as patents. We studied in this work the electrochemical generation of dissolved chlorine dioxide from an un-buffered solution of sodium chlorite and sodium chloride mixture in an un-divided electrochemical cell set-up with RuO(2)-coated-Ti anode and Pt-coated-Ti cathode under constant current mode. Various process parameters including feed flow rate (10 to 150 ml/min), feed solution pH (2.3 to 9.4), concentration of sodium chloride (0 to 170 mM), concentration of sodium chlorite (0 to 7.7 mM), and the applied current (100 to 1,200 mA) were optimized. Experiments were conducted by performing single pass experiments, with no circulation. The current efficiency and the power consumption were calculated for the optimized conditions, and compared with IrO(2) electrode of our previous investigation.

Destruction of commercial pesticides by cerium redox couple mediated electrochemical oxidation process in continuous feed mode.

Mediated electrochemical oxidation was carried out for the destruction of commercial pesticide formulations using cerium(IV) in nitric acid as the mediator electrolyte solution in a bench scale set up. The mediator oxidant was regenerated in situ using an electrochemical cell. The real application of this sustainable process for toxic organic pollutant destruction lies in its ability for long term continuous operation with continuous organic feeding and oxidant regeneration with feed water removal. In this report we present the results of fully integrated MEO system. The task of operating the continuous feed MEO system for a long time was made possible by continuously removing the feed water using an evaporator set up. The rate of Ce(IV) regeneration in the electrochemical cell and the consumption for the pesticide destruction was matched based on carbon content of the pesticides. It was found that under the optimized experimental conditions for Ce(III) oxidation, organic addition and water removal destruction efficiency of ca. 99% was obtained for all pesticides studied. It was observed that the Ce(IV) concentration was maintained nearly the same throughout the experiment. The stable operation for 6h proved that the process can be used for real applications and for possible scale up for the destruction of larger volumes of toxic organic wastes.

Experimental aspects of combined NOx and SO2 removal from flue-gas mixture in an integrated wet scrubber-electrochemical cell system.

The objective of this work was to study the effect of some operating conditions on the simultaneous removal of NO(x) and SO2 from simulated NO-SO2-air flue-gas mixtures in a scrubber column. The gaseous components were absorbed into 6M HNO3 electrolyte in the scrubber in a counter-current mode, and were oxidatively removed by the Ag(II) mediator oxidant electrochemically generated in an electrochemical cell set-up. The integration of the electrochemical cell with the scrubber set-up ensured continuous regeneration of the Ag(II) mediator and its repeated reuse for NO(x) and SO2 removal purpose, thereby avoiding: (1) the usage of chemicals continuously for oxidation and (2) the production of secondary waste. The influences of packing material (raschig glass rings, raschig poly(vinylidene) fluoride rings, Jaeger tri-pack perfluoroalkoxy spheres), feed concentrations of NO and SO2 (100-400 ppm NO and 100-400 ppm SO2), superficial gas velocity (0.061-0.61ms(-1)) and liquid velocity (0.012-0.048 ms(-1)) were investigated. The raschig glass rings with high surface area provided highest NO removal efficiency. NO and NO(x) showed decreasing abatement at higher feed concentrations. The removal of nitrogen components was faster and also greater, when SO2 co-existed in the feed. Whereas the gas flow rate decreased the removal efficiency, the liquid flow rate increased it for NO and NOx. The flow rate effects were analyzed in terms of gas/liquid residence time and superficial liquid velocity/superficial gas velocity ratio. SO2 removal was total under all conditions.

Studies on process parameters for chlorine dioxide production using IrO2 anode in an un-divided electrochemical cell.

Chlorine dioxide is potentially a powerful oxidant with environmentally compatible application in several strategic areas relating to pollution control typically for water disinfection, and its sustained production is a key factor for its successful application. Although increased attention has been paid for on-line chlorine dioxide generation by several chemical and electrochemical methods, the details are mostly confined as patents. We studied in this work the electrochemical generation of chlorine dioxide from an un-buffered solution of sodium chlorite and sodium chloride mixture in an un-divided electrochemical cell under constant current mode, with a view to optimize various process parameters, which have a direct bearing on the chlorine dioxide formation efficiency under laboratory conditions. The effect of feed flow rate (10-150 ml min(-1)), feed solution pH (2.3-5.0), concentration of sodium chloride (0-169.4mM), concentration of sodium chlorite (0-7.7 mM), and the applied current (100-1200 mA) on the formation of dissolved ClO(2) gas in solution and the pH of the product-containing solution was investigated by performing single pass experiments, with no circulation, in a cell set-up with Ti/IrO(2) anode and Ti/Pt cathode. The current efficiency and the power consumption were calculated for the optimized conditions.

Novel process for simultaneous removal of NO(x) and SO2 from simulated flue gas by using a sustainable Ag(I)/Ag(II) redox mediator.

The objective of this work is to develop a sustainable process for simultaneous removal of waste gases such as NO, NO2, and SO2 by an electrochemically generated Ag(I)/Ag(II) redox mediator system. High removal efficiency was achieved for NO and SO2 by the wet scrubbing method at room temperature and atmospheric pressure. This removal is achieved through oxidation and absorption by contacting the gaseous stream with redox mediator ions that offer specific or selective solubility for the solute gases to be recovered in a wet scrubber. The process parameters such as gas velocity, liquid velocity, Ag(I) concentration, and HNO3 concentration were investigated to explore the possibility of complete removal of waste gases. The Ag(I)/Ag(II)-based mediated electrochemical oxidation process proved to be quite effective for simultaneous removal of NO, NO(x), and SO2 from the simulated flue gas mixtures containing NO and SO2 over a wide concentration range of 100-400 ppm. Studies were carried out with individual gas components for the mixture, and the effect of input NO and input SO2 concentrations on the NO(x) and SO2 removal efficiencies at 20 degrees C was examined. Complete oxidation of NO to NO2 with 100% NO removal efficiency and 92% NO(x) removal efficiency was achieved along with 100% SO2 removal efficiency, highlighting a potentially far greater efficiency of the Ag(I)/Ag(II)-based system in functionality and selectivity. Active research work in this direction is anticipated in the near future.